First, some time when the dogs aren't watching, get out some cheddar cheese and cut up into small pieces, and put into a baggie. Then hide that baggie somewhere up high, out of sight for a moment.
We are assuming the dogs have not heard a whistle before, of course. Then, and for no reason apparent to the dogs, suddenly toot the whistle, and dole out pieces of cheese to each dog. Whistle, toot about three times in a row. At this point you are teaching the dogs the sound of the whistle, just like you would would conditioned them to the sound of the clicker. Three times is enough for now and let it go.
After few hours, when the dogs are relaxed and thinking other doggie thoughts, suddenly toot your whistle when you see one of the dogs sauntering toward you, and give that dog a piece of the cheese.
If any of the other dogs starts come to you, too, give a quick toot of the whistle and offer a piece of the cheese. If you have a dog who is a little bit slow about figuring out what is going on with the whistle and the cheese, then sit with that dog alone in a room, and do whistle/cheese three times.
On the second day, wait until you are in a room with no dogs present. Toot the whistle and the dogs should come running to get some cheese. The next progression is to go to another floor of the house, such as an upstairs bedroom or the basement. Toot the whistle and as soon as a dog comes running to you, give it about five pieces of cheese at once (bigger reward because the dog made a greater effort to find you).
By the third day, start taking this game out into the yard, play some fetch, etc., just having a great time, when suddenly, unexpectedly, you toot the whistle. Only give the cheese if the dogs come running promptly.
By day four, while you've had all the dogs out in the yard, sort of amble away from them and head toward the doorway to go into the house. You're not to the doorway yet, but you toot the whistle. All they see is your back, going away from them. As the dogs come running, give them a higher powered treat such as a lovely slice of roast beef (bigger reward because they aborted their playtime to come to you).
From here on, it's simply a matter of building distance, and then going back to the starting place to build in ever-increasing distractions.